Matt Damon's Jason Bourne is gone from this fourth installment in the series, so the first half-hour is filled with a lot of frantic exposition that creates a new character -- Jeremy Renner's Aaron Cross -- with some sort of vague and confusing connection to the government program that created Bourne. (If you're not completely up on the backstory from the first three Bourne movies, you're going to be lost for most of that, I fear.)
All you really need to know is that Edward Norton wants to shut down the program that created Cross and several other super-spies, and that shutdown will involve killing all of those spies. That sets Cross on the run with Rachel Weisz; he's sort of kidnapped her, because she's a doctor who can help him get hold of the medicine he needs to maintain his super-skills.
Renner handles the action stuff reasonably well, but his character lacks the "who am I?" hook of Jason Bourne, and Renner doesn't involve us emotionally or give us any reason to care about Aaron Cross. Edward Norton is visibly unhappy to be in this movie; you feel like he'd rather have his neck in the guillotine.
Worst of all, Tony Gilroy doesn't shoot action sequences nearly as well as either Doug Liman or Paul Greengrass, his predecessors in this franchise. There's a long, long, loooooong chase scene through Manila, and the first half
of the scene (the part before the motorcycles get involved) is impossible to
follow, because we have no idea where the characters are in relation to one
The Bourne movies were never great art, but they were reasonably entertaining action flicks; when they lost their central character, the franchise should have come to an end. Sadly, the only real Bourne legacy will be this movie, a sad attempt to make a few more bucks.